1. Field of the Invention
The present invention relates to an image file processing method, and more particularly to a method for decoding a portion of an image file.
2. Related Art
A digital camera captures an image by using an optical sensor, converts the image into a digital signal, and then stores the captured image as an image file in a digital file format. Currently, Joint Photographic Experts Group (JPEG) is one of the most commonly used image file formats, and image files in JPEG format have been used in most digital cameras and other digital photograph products.
After the image is captured, a user usually reviews the image file stored in the digital camera. However, no matter how high the resolution of the image in the digital camera is, the user can only view a reduced resolution image through a small-size display screen. Therefore, when the user intends to view a portion of range in the image in detail, the user may zoom in the image, so as to view details of the portion of the image.
However, even if it only needs to zoom in and present a portion of the range in the image to the user, the most direct processing method is to decode the entire image file back into a full resolution image, and then display the portion of the image designated by the user. This method requires provision of a memory capable of accommodating the full resolution image, resulting in large consumption of memory capacity, memory bandwidth accessing, and operation resource during image decoding. When the image resolution increases rapidly, it results in an increased burden of decoding.
In order to reduce the required memory capacity, it is considered that only a portion of the range in the image is decoded and displayed to the user. For relevant technologies, reference may be made to, for example, U.S. Pat. No. 7,480,418. As compared with the original file, the conventional method increases the size of the image file due to overhead, and affects the data compression ratio. Moreover, the processed image file needs more information than general image compression standard. It is not applicable to existing general decoders (for example, JPEG decoders), so that the compatibility is lost.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.